Within the context of the present invention, said approach phase exhibits:                an initial phase defined between a first point (known as the “final approach point”) and a second point (known as the “transition point”), during which phase the aircraft is guided according to a predetermined flight plan observing required navigational performance (“Required Navigation Performance” being a universally recognized English-language expression often abbreviated to RNP); and        a terminal phase defined between this transition point and the actual landing on a runway, during which phase the aircraft is guided along a line of approach.        
It is know that, in an international context in which air traffic is ever on the increase, aircraft flight paths are allocated flight lanes of increasingly narrow width. In order to be able to reduce this flight lane width, consideration is given in particular to certain aspects of said aircraft performance. The latter characteristics are in particular implemented during said initial phase of the approach phase between said final approach point and said transition point.
It is also known that the performance aspects that an aircraft needs to be able to observe in order to remain inside such a flight lane are of two types, namely:                guidance performance: the objective being to make the aircraft correctly follow a flight plan, that is to say to minimize a guidance error (known by its English-language term “Flight Technical Error” or FTE); and        navigation performance: the objective being to have a good estimate of the actual position of the aircraft, that is to say to minimize a position estimation error (“Position Estimation Error” being a universally acknowledged English-language term often abbreviated to PEE).        
In order to meet the above performance criteria it is therefore necessary to minimize the sum of these two errors FTE and PEE, namely a total error known by its English-language term “Total System Error” or TSE.
The ability to adhere to this TSE parameter is one of the requisite conditions that in particular will allow:                the aircraft to be flown in novel types of approach, over terrain containing obstacles or exhibiting landing restrictions;        simultaneous approaches to be made to runways that are situated close together; and        lower minimum landing decision types to be authorized.        
As a result, giving consideration to navigation and guidance performance of the RNP type in the aforementioned initial phase (between said final approach point and said transition point) makes it possible to lower the minimum decision heights by comparison with a customary non-precision approach, but does not make it possible to drop below a predetermined altitude, of 250 feet (approximately 75 meters) for example, which relates to said transition point.
From said transition point onward, said terminal phase of the approach phase can be implemented, guiding the aircraft along a line of approach which is consistent with a precision instrument landing approach using, for example, instruments of the ILS (the abbreviation for the recognized English term “Instrument Landing System”) or with a non-precision approach.
However, in situations such as these, at the transition (at said transition point) between the initial phase and the terminal phase, the change in guidance mode is generally performed somewhat abruptly, particularly as regards the guidance proper, and in terms of the display of corresponding information presented to the crew. This in particular gives rise to the following disadvantages:                discomfort to the passengers and the pilot;        pilot stress as the aircraft reacts sharply; and        during the initial phase, a lack of information presented to the pilot that will allow him to position the aircraft relative to a line of approach xLS (specified hereinbelow) and check that the position of the aircraft is consistent with this line xLS.        